Method for producing semiconductor chip

ABSTRACT

A method for producing a semiconductor chip is a method for producing a semiconductor chip that includes a substrate, a conductive portion formed on the substrate, and a microbump formed on the conductive portion, which includes a smooth surface formation process of forming a smooth surface on the microbump, and the smooth surface formation process includes a heating process of causing a reducing gas to flow in an inert atmosphere into a space where the semiconductor chips are arranged and heated at or higher than a temperature of a melting point of the microbump, and in the heating process, a pressure application member is mounted on the microbump and among principal surfaces of the pressure application member, a principal surface that contacts the microbump is a flat surface.

This is a continuation-in-part application of U.S. patent applicationSer. No. 15/449,361 filed Mar. 3, 2017. The disclosure of the priorapplication is incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a method for producing a semiconductorchip.

BACKGROUND

Conventionally, in a three-dimensional installation of semiconductorpackage, coupling between a semiconductor chip and a semiconductor chipor an interposer is performed by wire bonding. In place of the wirebonding, a three-dimensional installation technique, with whichsemiconductor chips are coupled with each other via a pass-throughelectrode and a bump, has been developed. The pass-through electrodenormally has a short connecting wire length (for example, 50 μm), and abump, via which electrodes are connected, is also required to bemicroscopic. A technique that handles such a bump pitch of less than 50μm is referred to as a microbump. As U.S. Pat. No. 9,136,159, a wiringlength between semiconductor chips can be dramatically shortened bycoupling the semiconductor chip and the semiconductor chip with thepass-through electrode and the microbump. Accordingly, a wiring delaytime that increases with miniaturization can be reduced.

SUMMARY

Here, lamination of a semiconductor chip and a semiconductor chip iscarried out by flip-chip implementation. However, as a plurality ofsemiconductor chips are laminated and bonded, problems such as aposition misalignment between the semiconductor chips occur. Inaddition, also when another electronic component or the like isimplemented to a semiconductor chip, it is required that bonding iscarried out in a more preferable manner.

Made in the light of such a circumstance, the present invention isintended to provide a method for producing a semiconductor chip in whichbonding of a semiconductor chip with another member can be carried outin a more preferable manner.

A method for producing a semiconductor chip according to an aspect ofthe present invention is a method for producing a semiconductor chipthat includes a substrate, a conductive portion formed on the substrate,and a microbump formed on the conductive portion, which includes asmooth surface formation process of forming a smooth surface on themicrobump, and the smooth surface formation process includes a heatingprocess of causing a reducing gas to flow in an inert atmosphere into aspace where the semiconductor chips are arranged and heated at or higherthan a temperature of a melting point of the microbump, and in theheating process, a pressure application member is mounted on themicrobump and among principal surfaces of the pressure applicationmember, a principal surface that contacts the microbump is a flatsurface.

This method for producing a semiconductor chip includes a smooth surfaceformation process of forming a smooth surface on the microbump. In theheating process, which is included in the smooth surface formationprocess, the reducing gas is caused to flow in the inert atmosphere intoa space where the semiconductor chips are arranged and is heated. Thus,an oxide film formed on a surface of the microbump is reduced andremoved. In addition, in the heating process, heated at or higher than atemperature of the melting point of the microbump, and thus themicrobump is molten and gets fluidity. Here, in the heating process, apressure application member is mounted on the microbump. Accordingly, asthe microbump is molten and gets fluidity, pressure of the pressureapplication member causes the microbump to be deformed as if it iscollapsed. Among principal surfaces of the pressure application member,a principal surface that contacts the microbump is a flat surface.Accordingly, in the microbump that has been molten, a portion pushed bythe pressure application member is formed as the smooth surface inaccordance with the shape of the flat surface of the pressureapplication member. When a semiconductor chip is bonded with anothermember, it is possible to carry out the bonding using a smooth surfaceof the microbump, enabling a preferable bonding to be carried out.

In the heating process, a pressure application member is mounted on aplurality of microbumps, and among the principal surfaces of thepressure application member, a principal surface that contacts theplurality of microbumps may be a flat surface. Thus, the pressureapplication member is capable of collectively applying pressure in astate where an identical flat surface is caused to contact the pluralityof microbumps. In this case, the smooth surfaces of the plurality ofmicrobumps form an identical flat surface to each other in accordancewith the flat surface of the pressure application member. Accordingly,it is possible to reduce unevenness of the height among the smoothsurfaces of the plurality of microbumps.

As the reducing gas, carboxylic acid may be applied. Thus, an oxide filmon the surface of the microbump is removed successfully.

The weight of the pressure application member may be from 0.0005 μg/μm²to 0.1 μg/μm² per cross-sectional area of the microbump. Thus, thepressure application member is capable of applying an appropriatepressure to remove the void on the microbump.

A spacer that has a certain thickness is arranged on the substrate andthe pressure application member may be pushed to contact the spacer.This causes the spacer to stop the pressure application member and thuscan prevent the microbump from being collapsed too much.

On the substrate, a microbump arrangement area, in which the pluralityof microbumps are aligned, is set, and the spacer may be arranged at anedge portion of the microbump arrangement area. This facilitates thework of arranging the spacer on the substrate.

A method for producing a semiconductor chip according to an aspect ofthe present invention is a method for producing a semiconductor chipthat includes a substrate, a conductive portion formed on the substrate,and a microbump formed on the conductive portion, which includes aheating process of causing a reducing gas to flow in an inert atmosphereinto a space where the semiconductor chips are arranged and heated at orhigher than a temperature of a melting point of the microbump, and inthe heating process, a pressure application member is mounted on themicrobump, and after the heating process, the pressure applicationmember is removed from the microbump.

In this method for producing a semiconductor chip, in the heatingprocess, the reducing gas is caused to flow in the inert atmosphere intoa space where the semiconductor chips are arranged, and is heated. Thus,an oxide film formed on a surface of the microbump is reduced andremoved. In addition, in the heating process, heated at or higher than atemperature of the melting point of the microbump, and thus themicrobump is molten and gets fluidity. Here, in the heating process, apressure application member is mounted on the microbump. Accordingly, asthe microbump is molten and gets fluidity, pressure of the pressureapplication member causes the microbump to be deformed as if it iscollapsed. Accordingly, in the microbump that has been molten, a portionpushed by the pressure application member is formed as a smooth surfaceby being collapsed. When a semiconductor chip is bonded with anothermember, it is possible to carry out the bonding using a smooth surfaceof the microbump, enabling a preferable bonding to be carried out.

According to the present invention, a method for producing asemiconductor chip in which bonding with another member can bepreferably carried out can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view that presents an embodiment of asemiconductor package;

FIG. 2 is a flow chart that presents a procedure of a method forproducing a semiconductor package;

FIGS. 3A and 3B are schematic sectional views that present semiconductorchips being laminated;

FIG. 4A is a schematic sectional view that presents semiconductor chipsbeing laminated, and FIG. 4B is a schematic sectional view that presentssemiconductor chips being coupled with each other;

FIG. 5 is a schematic sectional view that presents a microbump before asmooth surface formation process is carried out and the microbump aftera smooth surface formation process is carried out;

FIG. 6 is a flow chart that presents a procedure of the smooth surfaceformation process (void removal process);

FIGS. 7A to 7G are schematic sectional views that present the procedureof the smooth surface formation process (void removal process);

FIGS. 8A to 8G are schematic sectional views that present the procedureof the smooth surface formation process (void removal process) accordingto a variation;

FIG. 9 is a graph that presents a profile of the temperature andpressure in the heating furnace;

FIGS. 10A to 10C are schematic sectional views that present theprocedure of the smooth surface formation process (void removalprocess);

FIGS. 11A and 11B are schematic sectional views that present theprocedure of the smooth surface formation process (void removalprocess);

FIGS. 12A and 12B are schematic views that present the arrangement oflight-emitting devices;

FIGS. 13A to 13C are schematic views that present the procedure offorming the microbumps;

FIGS. 14A to 14C are schematic views that present the procedure ofimplementing the light-emitting devices to the semiconductor chips;

FIGS. 15A and 15B are schematic views that present an issue at the timeof implementing the light-emitting devices to the semiconductor chips;

FIG. 16 is a table that presents combinations of the materials of theconductive portion and the plating film of the light-emitting device andthe materials of the conductive portion and the plating film of thesemiconductor chip;

FIG. 17 is a table that presents experiment results of Examples andComparative Examples; and

FIG. 18 is a table that presents experiment results of Examples andComparative Examples.

Now, preferred embodiments of a method for producing a semiconductorpackage according to an aspect of the present invention will bedescribed in detail with reference to the drawings. It should be notedthat elements that are identical or elements that have an identicalfunction are designated by the same reference numerals, and redundantdescriptions will be curtailed.

FIG. 1 is a schematic sectional view that presents an embodiment of asemiconductor package. As presented in FIG. 1, a semiconductor package100 includes a laminate 2 constituted by laminating three or more (it isthree here) semiconductor chips 1, an organic substrate 4 electricallyconnected with the laminate 2 via a solder ball 3, and a molded portion6 formed by covering with a mold resin the laminate 2 mounted on theorganic substrate 4. It should be noted that an inner space of themolded portion 6 is filled with an underfill 7 so that gaps between thesemiconductor chips 1 of the laminate 2 are filled. In the presentembodiment, the laminate 2 is constituted by laminating thesemiconductor chip 1A, the semiconductor chip 1B, and the semiconductorchip 1C in a vertical direction. The semiconductor chip 1A and thesemiconductor chip 1B are bonded via a bonded portion 8 bonded bymelting the microbump. The semiconductor chip 1C and the semiconductorchip 1B are bonded via the bonded portion 8 bonded by melting themicrobump.

For example, as presented in FIG. 4A, the semiconductor chips 1 beforebonded include a substrate 11, conductive portions 12 formed on thesubstrate 11, and microbumps 13 formed on the conductive portions 12.The substrate 11 is composed of, for instance, a semiconductor chip suchas a silicon (Si) chip, a silicon (Si) interposer, and the like. Itshould be noted that the semiconductor chip 1A and the semiconductorchip 1C are provided with the conductive portions 12 formed only on oneprincipal surface. The semiconductor chip 1B is provided with theconductive portions 12 formed on both principal surfaces. In addition,the conductive portions 12 formed on both principal surfaces of thesemiconductor chip 1B are connected to each other via through holeelectrodes 19 that extend in a thickness direction of the substrate 11.

The plurality of conductive portions 12 are formed on the principalsurfaces of the substrate 11. The conductive portions 12 are arrangedwith a predetermined pitch on the principal surfaces of the substrate11. The conductive portion 12 includes an electrode pad 14 formed on theprincipal surface of the substrate 11 and a barrier metal layer 16formed on an upper surface of the electrode pad 14. It should be notedthat a portion of the principal surface of the substrate 11 on which theconductive portions 12 are not formed is covered with an insulationlayer 17 (see FIG. 5). As materials that compose the barrier metal layer16, for example, Ni, Ni compound (such as NiP), and the like are used.As materials that compose the insulation layer 17, for instance, SiO,SiN, polyimide and the like are used.

The microbump 13 is formed on the barrier metal layer 16 of theconductive portion 12. The microbump 13 may include Sn, Ag, Cu, Ag—Cu,Bi, In, and the like as materials that compose the microbump 13, and analloy of any two or more of these materials may be used. In particular,the microbump 13 may include Sn as a principal component. The microbump13 may be formed by plating for example. Alternatively, the microbump 13may be formed by using a micro ball made of a solder alloy, and it maybe formed by printing a paste. It should be noted that a bump that isless than 50 μm in diameter seen from above is referred to as amicrobump.

As presented in FIG. 5, the microbump 13 has a spherical surfaceimmediately after being formed on the substrate 11. By providing apredetermined processing to the microbump 13, a smooth surface 13 a isformed on the microbump 13. The smooth surface 13 a is constituted witha flat surface extending in a horizontal direction at a top of themicrobump 13. It should be noted that an example of the processingdetail for forming the smooth surface 13 a will be described later. Aheight of the microbump 13, in other words, a dimension between thesmooth surface 13 a and the upper surface of the conductive portion 12can be set in a range of 5 to 50 μm.

Next, a method for producing the semiconductor package 100 according tothe present embodiment will be described with reference to FIGS. 2 to 9.

As presented in FIG. 2, first, a semiconductor chip preparation process(step S1), in which the semiconductor chip 1 is prepared by forming themicrobump 13 on the substrate 11, is carried out. This prepares thesemiconductor chip 1A, the semiconductor chip 1B, and the semiconductorchip 1C. However, in this stage, the smooth surface 13 a has not beenformed on the microbump 13.

Next, a smooth surface formation process (step S2), in which the smoothsurface 13 a is formed on the microbump 13, is carried out. In addition,the smooth surface formation process S2 corresponds to a void removalprocess, in which a void 22 is removed from an inside of the microbump13.

A detail of the smooth surface formation process (void removal process)S2 will now be described with reference to FIG. 6.

As presented in FIGS. 6 and 7A, a pressure application member placementprocess (step S20), in which a pressure application member 21 is placedon the microbump 13, is carried out. In this manner, the semiconductorchip 1 is arranged inside of a heating furnace in a state where thepressure application member 21 is placed thereon. It should be notedthat the subsequent description will be given with reference to aprofile of a temperature and pressure in the heating furnace presentedin FIG. 9 as appropriate. It should be noted that in FIG. 9, the solidline denotes the temperature in the heating furnace and the dashed linedenotes the pressure in the heating furnace.

As presented in FIG. 10A, in the pressure application member placementprocess S20, the pressure application member 21 may be mounted on theplurality of microbumps 13. At this time, among the principal surfacesof the pressure application member 21, a principal surface 21 a thatcontacts the plurality of microbumps 13 is a flat surface. In otherwords, the principal surface 21 a, which constructs an identical flatsurface, contacts the plurality of microbumps 13. It is to be noted thatthe plurality of microbumps 13 are arranged in the right and leftdirection on the surface of the sheet of paper and the front and backdirection on the surface of the sheet of paper of FIG. 10A. Accordingly,the pressure application member 21 is mounted on the plurality ofmicrobumps 13, which are arranged in the right and left direction on thesurface of the sheet of paper and the front and back direction on thesurface of the sheet of paper. The single pressure application member 21may be used for the single semiconductor chip 1, and the plurality ofpressure application members 21 may be used for the plurality ofsemiconductor chips 1. In other words, the pressure application member21 may be mounted on all of the microbumps 13 in the semiconductor chip1. Alternatively, the single pressure application member 21 may bemounted on each segment of the semiconductor chip 1 that has beendivided into a plurality of segments. However, the single pressureapplication member 21 may be mounted on the single microbump 13.

As materials that compose the pressure application member 21 mounted onthe microbump 13, it is preferable that materials that do not react withthe microbump 13 are adopted. For instance, Si, SiO₂, SiN, and the likeare adopted as materials that compose the pressure application member21. In addition, among the principal surfaces of the pressureapplication member 21, a principal surface 21 a that contacts themicrobump 13 is preferably constructed as a flat surface. It is becausethe pressure application member 21 becomes hard to remove because, forexample, if a protrusion or the like is formed on the principal surface21 a, it is caught with the microbump 13. It is preferable that the onlypressure that the pressure application member 21 applies to themicrobump 13 is the own weight of the pressure application member 21itself. More specifically, it is preferable that the pressure is from0.0005 μg/μm² to 0.1 μg/μm² per cross-sectional area of the microbump.For instance, if the pressure or the height of the pressure applicationmember 21 is controlled with a method such as flip-chip implementation,the pressure applied to the pressure application member 21 is reducedwhen the microbump 13 changes from a solid to a liquid (when it changesfrom FIGS. 7B to 7C), and hence a misalignment occurs in the position ofthe pressure application member 21. With respect to a small bump such asthe microbump 13, a slight misalignment causes excessive pressure to beapplied.

Next, a decompression process (step S21), in which a space in theheating furnace where the semiconductor chips 1 are arranged isdecompressed, is carried out. In the decompression process S21, insideof the heating furnace is vacuumed so that a reduced-pressure atmosphereis created. Oxygen remaining in the heating furnace causes the microbump13 to be oxidized. Accordingly, it is preferable that inside of theheating furnace is decompressed to a decompressed state of atmosphericpressure (from 1.01×10̂5 Pa to 1×10̂3 Pa or less, in particular, 5 Pa orless). This reduces the pressure in the heating furnace (see P1 portionof the graph of FIG. 9). Inert gas is introduced in the heating furnaceof the reduced-pressure atmosphere. This raises the pressure in theheating furnace (see P2 portion of the graph of FIG. 9). When thetemperature inside the heating furnace is raised to a temperature rangeof melting temperature or higher (melting point or higher) of themicrobump 13, inert gas prevents further oxidization of the surface ofthe microbump 13 and realizes melting of the microbump 13, thusfunctioning as a heating medium in the heating furnace. As such inertgas, for example, nitrogen (N₂) gas, argon (Ar) gas, and the like can beused.

Next, a heating process (step S22), in which reducing gas is caused toflow in the heating furnace in an inert atmosphere and heated at atemperature of melting point or higher of microbump 13, is carried out.The heating process S22 is carried out after the inert gas is introducedinto the heating furnace or substantially simultaneously withintroduction of the inert gas. In the heating process S22, thetemperature inside the heating furnace is raised at a predetermined rateof temperature rise (for instance 35 to 45° C./minute), and thetemperature inside the heating furnace in a state where the inert gashas been introduced is raised to the temperature range of melting pointor higher of the microbump 13. For example, when the bump is composed ofSn—Ag—Cu alloy, the melting point is approximately 220 to 230° C.although depending upon the composition of the alloy, and hence thetemperature inside the heating furnace is raised to the temperaturerange of such temperature or higher.

It is preferable that the introduction of reducing gas is carried outbefore or after at the temperature at which a reduction reaction of anoxide film 23 begins. While maintaining the temperature inside theheating furnace (temperature T1 of FIG. 9) at the temperature at which areduction reaction begins or higher, reducing gas with an appropriatedensity and flow rate is continued to be supplied. This allows the oxidefilm 23 existing on the surface of the microbump 13 to be reduced andremoved. As a reducing gas, for example, carboxylic acid (formic acid)is applied. Examples of carboxylic acid include lower carboxylic acidsuch as formic acid, acetic acid, acrylic acid, and propionic acid. Ifformic acid is used as a reducing gas, it is preferable that formic acidis introduced when the temperature inside the heating furnace becomesabout 110° C. Even if formic acid is introduced at a temperature atwhich a reduction reaction begins or lower, the reaction does notproceed, and if the temperature is too high, the microbump 13 is heatedwith the oxide film 23 on the surface being left and hence the pressureinside the void 22 rises. Removing the oxide film 23 in a state wherethe pressure inside the void 22 has excessively risen releases thepressure inside the void 22 all at once and the microbump 13 that hasbeen liquefied may scatter. Accordingly, the temperature T1 at which thereducing reaction begins may be maintained for a predetermined length oftime, and in a stage where the oxide film 23 has been sufficientlyremoved, the temperature of the heating furnace may be maintained at thetemperature T2, which is the melting point or higher of the microbump 13(see FIG. 9).

When the microbump 13 has been molten, the void 22 has been removed, andthe smooth surface 13 a has been formed, a temperature drop process(step S23), in which the temperature of the heating furnace is dropped,is carried out. More specifically, in the heating furnace where thetemperature T2, which is the melting point or higher of the microbump13, is maintained, after the microbump 13 is exposed to formic acid fora predetermined length of time (for instance, 0.5 to 3 minutes), theformic acid introduced into the heating furnace is exhausted byvacuuming. After the formic acid introduced into the heating furnace isexhausted or substantially simultaneously with the exhaust of the formicacid, inside the heating furnace is dropped at a predetermined rate oftemperature drop (for example, −5 to −40° C./minute). It should be notedthat in FIG. 9, vacuuming is carried out before the temperature in theheating furnace is dropped. However, when the temperature in the heatingfurnace is dropped to a temperature range where molten bump issolidified to some extent, an inert gas such as nitrogen gas and argongas may be introduced into the heating furnace to return to theatmospheric pressure.

By carrying out the heating process S22 and the temperature drop processS23 as described above, as presented in FIGS. 7B to 7G, the void 22 isremoved from the microbump 13 and the smooth surface 13 a is formed onthe microbump 13. In other words, by carrying out heating in anatmosphere of reducing gas, the oxide film 23 formed on the surface ofthe microbump 13 is reduced and removed (see FIG. 7B). Then, by applyingheat at or higher than a temperature of the melting point of themicrobump 13, the microbump 13 is molten. Thus, the pressure of thepressure application member 21 deforms the microbump 13 as if it iscollapsed. Due to this, in accordance with the shape of the principalsurface 21 a of the pressure application member 21, a shapecorresponding to the smooth surface 13 a is formed on the microbump 13(see FIGS. 7C to 7F). In addition, the microbump 13 that has been moltenis pushed by the pressure application member 21 and flows, and thus thevoid 22 in the microbump 13 rises and escapes to outside (see FIGS. 7Cto 7F). By returning the temperature in the heating furnace, themicrobump 13 is cooled and hardened. Thus, the smooth surface 13 a isformed on the microbump 13 (see FIG. 7G).

As presented in FIG. 10, in the heating process S22, the pressureapplication member 21 is in a state where it is mounted on the pluralityof microbumps 13. As presented in FIG. 10B, the pressure applicationmember 21 collectively applies pressure in a state where an identicalflat surface is caused to contact the plurality of microbumps 13. Thus,the plurality of microbumps 13 are deformed by the pressure applicationmember 21 as if they are collectively collapsed. Due to this, inaccordance with the shape of the principal surface 21 a of the pressureapplication member 21, a shape corresponding to the smooth surface 13 ais formed on the plurality of microbumps 13. By returning thetemperature in the heating furnace, the microbump 13 is cooled andhardened. Thus, the smooth surface 13 a is formed on the plurality ofmicrobumps 13. After that, as presented in FIG. 10C, the pressureapplication member 21 is removed from the plurality of microbumps 13.

Returning to FIG. 2, after the smooth surface formation process S2 hasbeen completed with regard to each of the semiconductor chips 1, alamination process (step S3), in which three or more of thesemiconductor chips 1 are laminated by overlaying the microbump 13 ofone of the semiconductor chips 1 on the microbump 13 of another one ofthe semiconductor chips 1, is carried out. In the present embodiment, inthe lamination process S3, the smooth surface 13 a is formed on themicrobump 13 of one of the semiconductor chips 1 and another one of thesemiconductor chips 1. Then, the microbump 13 of one of thesemiconductor chips 1 contacts the microbump 13 of another one of thesemiconductor chips 1 on the smooth surface 13 a. In the laminationprocess S3, all the semiconductor chips 1 are overlaid in a state wherethe microbumps 13 are not bonded to each other.

More specifically, as presented in FIGS. 3A and 3B, the microbump 13 ofthe semiconductor chip 1B is overlaid on the microbump 13 of thesemiconductor chip 1C, which is the bottommost. At this time, the smoothsurface 13 a of the microbump 13 of the semiconductor chip 1B isoverlaid on the smooth surface 13 a of the microbump 13 of thesemiconductor chip 1C. In addition, the microbump 13 of thesemiconductor chip 1C and the microbump 13 of the semiconductor chip 1Bare not bonded to each other, and they are in a state of simplycontacting each other.

Next, as presented in FIGS. 3B and 4A, the microbump 13 of thesemiconductor chip 1A, which is the uppermost, is overlaid on themicrobump 13 of the semiconductor chip 1B, which is the second from thebottom. At this time, the smooth surface 13 a of the microbump 13 of thesemiconductor chip 1A is overlaid on the smooth surface 13 a of themicrobump 13 of the semiconductor chip 1B. In addition, the microbump 13of the semiconductor chip 1B and the microbump 13 of the semiconductorchip 1A are not bonded to each other, and they are in a state of simplycontacting each other.

After completing the lamination process S3, a bonding process (step S4),in which the semiconductor chips 1 are bonded to each other via themicrobumps 13 by heating to melt the microbumps 13, is carried out. Inthe bonding process S4, all the microbumps 13 are collectively molten byheating once and all the semiconductor chips 1 are collectively bonded.In addition, in the bonding process S4, the microbumps 13 of thesemiconductor chips 1 are molten in a reducing atmosphere.

More specifically, as presented in FIG. 4A, a lamination in a statewhere the semiconductor chip 1A, the semiconductor chip 1B, and thesemiconductor chip 1C are laminated via the microbumps 13 is arranged inthe heating furnace. Then, by heating the lamination in the heatingfurnace, all the microbumps 13 in the lamination are molten and themicrobumps 13 that have been contact each other are collectively bonded.Thus, the semiconductor chip 1A, the semiconductor chip 1B, and thesemiconductor chip 1C are be bonded via the bonded portion 8 at whichtwo of the microbumps 13 are molten and bonded to each other, aspresented in FIG. 4B.

After completing the bonding process S4, a semiconductor packagecreation process (step S5), in which the semiconductor package 100 iscreated, is carried out. In the semiconductor package creation processS5, the laminate 2, which is obtained in the bonding process S4, iscoupled to the organic substrate 4, and the laminate 2 is covered withthe molded portion 6. With above, the semiconductor package 100 iscompleted and the method for producing presented in FIG. 2 terminates.

Next, an operation and effect of the method for producing thesemiconductor package 100 according to the present embodiment will bedescribed.

The method for producing the semiconductor chip 1 includes the smoothsurface formation process S2 of forming the smooth surface 13 a on themicrobump 13. In the heating process S22 included in the smooth surfaceformation process S2, the reducing gas is caused to flow in an inertatmosphere into a space where the semiconductor chips 1 are arranged,and is heated. Thus, the oxide film 23 formed on a surface of themicrobump 13 is reduced and removed. In addition, in the heating processS22, heated at a temperature of the melting point of the microbump 13 orhigher, and thus the microbump 13 gets fluidity by being molten. Here,in the heating process S22, the pressure application member 21 ismounted on the microbump 13. Accordingly, as the microbump 13 is moltenand gets fluidity, pressure of the pressure application member 21 causesthe microbump 13 to be deformed as if it is collapsed. Among theprincipal surfaces 21 a of the pressure application member 21, theprincipal surface 21 a that contacts the microbump 13 is a flat surface.Accordingly, in the microbump 13 that has been molten, a portion pushedby the pressure application member 21 is formed as the smooth surface 13a in accordance with the shape of the pressure application member 21.When the semiconductor chip 1 is bonded with another member, it ispossible to carry out the bonding using the smooth surface 13 a of themicrobump 13, enabling a preferable bonding to be carried out.

In the heating process S22, the pressure application member 21 ismounted on the plurality of microbumps 13, and among the principalsurfaces of the pressure application member 21, the principal surface 21a that contacts the microbump 13 is a flat surface. Thus, the pressureapplication member 21 is capable of collectively applying pressure in astate where an identical flat surface is caused to contact the pluralityof microbumps 13. In this case, the smooth surfaces 13 a of theplurality of microbumps 13 form an identical flat surface to each otherin accordance with the flat surface of the pressure application member21. Accordingly, it is possible to reduce unevenness of the height amongthe smooth surfaces 13 a of the plurality of microbumps 13.

When the smooth surface 13 a is formed by grinding, there is apossibility of damage being caused by force acting on the microbump 13and the conductive portion 12. On the other hand, if the smooth surface13 a is formed by using the pressure application member 21 as in theembodiment described above, damage on the microbump 13 and theconductive portion 12 can be suppressed.

In the method for producing the semiconductor package 100, in theheating process S22, the reducing gas is caused to flow in an inertatmosphere into a space where the semiconductor chips 1 are arranged.Thus, the oxide film 23 formed on a surface of the microbump 13 isreduced and removed. In addition, heated at a temperature of the meltingpoint of the microbump 13 or higher, and thus the microbump 13 getsfluidity by being molten. Here, in the heating process S22, the pressureapplication member 21 is mounted on the microbump 13. Accordingly, asthe microbump 13 is molten and gets fluidity, pressure of the pressureapplication member 21 causes the microbump 13 to be deformed as if it iscollapsed. The deformation generates a flow in the microbump 13 and thevoid 22 flows in the microbump 13. Thus, the void 22 flowing in themicrobump 13 to escape from the microbump 13 to outside and the void 13is removed. With above, the void 22 in the microbump 13 can be removedwith ease.

As the reducing gas, carboxylic acid may be applied. Thus, the oxidefilm 23 on the surface of the microbump 13 is removed successfully.

The weight of the pressure application member 21 may be from 0.0005μg/μm² to 0.1 μg/μm² per cross-sectional area of the microbump 13. Thus,the pressure application member 21 is capable of applying an appropriatepressure to remove the void 22 on the microbump 13.

In the method for producing the semiconductor package 100, in thelamination process S3, of one of the semiconductor chips 1 and anotherone of the semiconductor chips 1, the smooth surface 13 a is formed onthe microbump 13 of at least one of them, and the microbump 13 of one ofthem contacts the microbump 13 of the other one of them on the smoothsurface 13 a. In this manner, by overlaying the microbumps 13 of eachother using the smooth surface 13 a, one of the semiconductor chips 1and the other one of the semiconductor chips 1 can be laminated withaccurate positioning. This allows even a multitude of semiconductorchips 1 of three or more to be laminated in a state with accuratepositioning between the semiconductor chips 1. By carrying out thebonding process S4 in this state, the semiconductor chip 1 and thesemiconductor chip 1 can be bonded with accurate positioning.

In the lamination process S3, all the semiconductor chips 1 are overlaidin a state where the microbumps 13 are not bonded to each other, and inthe bonding process S4, all the microbumps 13 are collectively molten byheating once and all the semiconductor chips 1 are collectively bonded.This can prevent the bonded portion 8, which has been bonded by meltingthe microbump 13 once, from being repeatedly heated. Accordingly,reduction of the strength of the bonded portion 8 can be prevented.

Both the microbump 13 of one of the semiconductor chips 1 and themicrobump 13 of another one of the semiconductor chips 1 contain Sn, andin the bonding process S4, the microbump 13 of one of the semiconductorchips 1 and the microbump 13 of another one of the semiconductor chips 1may be molten in a reducing atmosphere. Thus, the oxide film 23 formedon the surface of the microbumps 13 of each other is reduced andremoved. In addition, since the microbumps 13 of each other contain Sn,they are mixed with each other and integrated with melting. With this,by an action of surface tension of the microbump 13 that has beenliquefied, a position misalignment between one of the semiconductorchips 1 and the other one of the semiconductor chips 1 (self-alignmenteffect).

In the method for producing the semiconductor chip 1, the reducing gasis caused to flow in an inert atmosphere into a space where thesemiconductor chips 1 are arranged, and is heated in the heating processS22. Thus, the oxide film 23 formed on a surface of the microbump 13 isreduced and removed. In addition, in the heating process S22, heated ata temperature of the melting point of the microbump 13 or higher, andthus the microbump 13 gets fluidity by being molten. Here, in theheating process S22, the pressure application member 21 is mounted onthe microbump 13. Accordingly, as the microbump 13 is molten and getsfluidity, pressure of the pressure application member 21 causes themicrobump 13 to be deformed as if it is collapsed. Accordingly, in themicrobump 13 that has been molten, a portion pushed by the pressureapplication member 21 is formed as the smooth surface 13 a by beingcollapsed. When the semiconductor chip 1 is bonded with another member,it is possible to carry out the bonding using the smooth surface 13 a ofthe microbump 13, enabling a preferable bonding to be carried out.

The present invention is not to be limited to the embodiment describedabove.

For instance, as presented in FIG. 8, a spacer 26 that has a certainthickness is arranged on the substrate 11 and the pressure applicationmember 21 may be pushed to contact the spacer 26. This causes the spacer26 to stop the pressure application member 21 and thus can prevent themicrobump 13 from being collapsed too much. For example, before heated,the spacers 26 are arranged on the both sides of the microbump 13 andthe pressure application member 21 is mounted on the microbump 13 (seeFIG. 8A). In this state, heated in a reducing atmosphere and the oxidefilm is removed (see FIG. 8B). The, when the microbump 13 is molten, thepressure application member 21 drops and contacts the upper surface ofthe spacer 26 (see FIG. 8C). Thus, the pressure application member 21 issupported by the spacer 26 and does not drop any further. On the otherhand, in the microbump 13 that has been molten, a flow is generated dueto an impact of the pressure application member 21 and the void 22 risesand is removed (see FIGS. 8D to 8G).

As presented in FIG. 11A, when the pressure application member 21 ismounted on the plurality of microbumps 13, the spacer 26 may be arrangedonly in a position that corresponds to the edge portion of the pressureapplication member 21. In this embodiment, on the substrate 11, amicrobump arrangement area W, in which the plurality of microbumps 13are aligned, is set, and the spacer 26 is arranged at the edge portionof the microbump arrangement area W. It is to be noted that although inFIG. 11A, only a pair of the spacers 26 arranged in the right and leftdirection on the surface of the sheet of paper is presented, a pair ofthe spacers 26 may also be arranged in the front and back direction onthe surface of the sheet of paper. This facilitates the work ofarranging the spacer 26 on the substrate 11. Alternatively, as presentedin FIG. 11B, the spacer 26 may be arranged in a gap between eachmicrobump 13. It is to be noted that as in FIG. 11B, the spacer 26 maybe arranged in some of the gaps even if the spacer 26 is not arranged inall of the gaps.

In addition, in the embodiment described above, the microbump 13 of thesemiconductor chip 1 of the lower side has the smooth surface 13 a andthe microbump 13 of the semiconductor chip 1 of the upper side has thesmooth surface 13 a. Accordingly, the smooth surface 13 a of themicrobump 13 of the upper side is mounted on the smooth surface 13 a ofthe microbump 13 of the lower side. However, the smooth surface 13 a maybe formed on any one of the microbump 13 of the upper side and themicrobump 13 of the lower side and the smooth surface 13 a may not beformed on the other side.

In the embodiment described above, another member to be bonded with asemiconductor chip was another semiconductor chip. In place of this,another thing may be adopted as another member to be bonded. Forexample, an electronic component may be adopted as another member to bebonded. A light-emitting device may be adopted as an electroniccomponent.

A component of an LED display can be constituted by bonding asemiconductor chip with a plurality of light-emitting devices. A pixelof an LED (light-emitting display) is constituted with a light-emittingdevice that is a natural light-emitting device, in contrast with amethod in which light of backlight is controlled by a transmissiveliquid crystal such as an LCD (liquid crystal display), for instance.Thus, an LED display has features of high brightness, enhanced life, andwide view angle. In order to increase the number of pixels in such anLED display, the light-emitting device may be reduced in size. When alight-emitting device is implemented to a semiconductor chip, a methodto implement light-emitting devices on a basis of one by one has beenadopted. However, with such the method, the lead time of implementationincreases as the light-emitting device gets smaller. For this reason, amethod to collectively implement light-emitting devices is examined.

More specifically, as presented in FIG. 12, a plurality oflight-emitting devices 50 are fixed in a predetermined alignment on anupper surface of a fixture 51. On the fixture 51, red light-emittingdevices 50A, green light-emitting devices 50B, and blue light-emittingdevices 50C are fixed in a predetermined alignment pattern. Thelight-emitting device 50 includes a conductive portion 53 and a platingfilm 52 formed on the conductive portion 53. The fixture 51 is composedof, for example, a glass plate that includes a UV release sheet on afixed surface and the like. Thus, after the light-emitting device 50 isimplemented to the semiconductor chip, the light-emitting device can bereleased from the fixture 51 by irradiating UV to the fixture 51.

When a fine light-emitting device of several tens of μm is implemented,printing of conventional solder paste is difficult. Accordingly, platingis formed on the conductive portion of the semiconductor chip by theplating method, and a method to bond the semiconductor chip with thelight-emitting device via the plating is adopted. More specifically, aspresented in FIG. 13A, a semiconductor chip 60, where conductiveportions 62 are formed on a substrate 61, is prepared. Next, aspresented in FIG. 13B, a plating film 63 is formed on the conductiveportion 62. After that, the plating film 63 is molten by heating thesemiconductor chip 60 in a reducing atmosphere. Thus, as presented inFIG. 13C, a plurality of microbumps 64 as bonding electrodes are formed.

Here, as presented in FIG. 15A, the plurality of microbumps 64 havevariations in thickness. In case where the light-emitting devices 50 arecollectively implemented to such the microbumps 64, as presented in FIG.15B, some of the light-emitting devices 50 are not bonded with thinmicrobumps 64, meanwhile some of the light-emitting devices 50 arebonded with thick microbumps 64.

In contrast, the method for producing the semiconductor chip 60 includesa smooth surface formation process of the same content as the method forproducing the semiconductor chip 1 described above. In the heatingprocess, which is included in the smooth surface formation process, thereducing gas is caused to flow in the inert atmosphere into a spacewhere the semiconductor chips 60 are arranged and is heated. Thus, anoxide film formed on a surface of the microbump 64 is reduced andremoved. In addition, in the heating process, heated at or higher than atemperature of the melting point of the microbump 64, and thus themicrobump 64 is molten and gets fluidity. Here, in the heating process,as presented in FIG. 14A, a pressure application member 70 is mounted onthe microbumps 64. Accordingly, as the microbump 64 is molten and getsfluidity, pressure of the pressure application member 70 causes themicrobump 64 to be deformed as if it is collapsed. Among principalsurfaces of the pressure application member 70, a principal surface 70 athat contacts the microbump 64 is a flat surface. Accordingly, in themicrobump 64 that has been molten, a portion pushed by the pressureapplication member 70 is formed as a smooth surface 64 a in accordancewith the shape of the pressure application member 70. As presented inFIG. 14B and FIG. 14C, when the semiconductor chip 60 and thelight-emitting devices 50 are collectively bonded together, it ispossible to carry out the bonding using the smooth surface 64 a of themicrobump 64, enabling a preferable bonding to be carried out.

In addition, in the heating process, the pressure application member 70is mounted on the plurality of microbumps 64, and among the principalsurfaces of the pressure application member 70, the principal surface 70a that contacts the plurality of microbumps 64 is a flat surface. Thus,the pressure application member 70 is capable of collectively applyingpressure in a state where an identical flat surface is caused to contactthe plurality of microbumps 64. In this case, the smooth surfaces 64 aof the plurality of microbumps 64 form an identical flat surface to eachother in accordance with the flat surface of the pressure applicationmember 70. Accordingly, it is possible to reduce unevenness of theheight among the smooth surfaces 64 a of the plurality of microbumps 64.Thus, as presented in FIG. 14C, when the plurality of light-emittingdevices 50 are collectively bonded with the semiconductor chip 60, it ispossible to prevent occurrence of the microbump 64 that is not connectedto the light-emitting device 50. In addition, the microbump 64 is moltenby being heated in the reducing atmosphere. Thus, the smooth surface ofthe microbump 64 can be formed with a low weight.

FIG. 16 is a table that presents combinations of the materials of theconductive portion 53 and the plating film 52 of the light-emittingdevice 50 and the materials of the conductive portion 62 and the platingfilm 63 of the semiconductor chip 60. In case where a good connectivityis obtained, a circle (∘) is given. As presented in FIG. 16, if theplating film 52 of the light-emitting device 50 contains Sn, the platingfilm 63 of the semiconductor chip 60, regardless of the material, iscapable of improving the connectivity between the light-emitting device50 and the semiconductor chip 60. In addition, if the plating film 63 ofthe semiconductor chip 60 contains Sn, the plating film 52 of thelight-emitting device 50, regardless of the material, is capable ofimproving the connectivity between the light-emitting device 50 and thesemiconductor chip 60.

EXAMPLES

Examples of the present invention will be described next. However, thepresent invention is not to be limited to the Examples described below.

Examples 1 to 7

As Example 1, a semiconductor chip that includes a microbump as followswas produced. First, a substrate was provided with Cu plating, Niplating, and Sn plating using an electrolytic plating process. Afterthis was arranged in a heating furnace, an atmosphere pressure in theheating furnace was adjusted and density and flow rate of nitrogen andformic acid gas to be supplied to the heating furnace were adjusted.This caused a sample of the semiconductor chip on which a plating filmwas molten and the microbump was formed to be created. The Cu platinglayer is 17 μm high, the Ni plating layer is 3 μm high, the microbump is15 μm high, and the microbump is 35 μm in diameter. A void was observedin the microbump when the sample was observed by transmission X-ray.This sample and a pressure application member were prepared. Thepressure application member was an Si wafer that includes an SiO₂ film.The Si wafer was mounted on the microbump so that the SiO₂ surfacecontacted the bump. The weight of the pressure application member was0.0005 μg/μm² per cross-sectional area of the microbump. It should benoted that the spacer as presented in FIG. 8 was not provided. After thesemiconductor chip in a state where the pressure application member wasmounted thereon was arranged in the heating furnace, inside of theheating furnace was vacuumed to 5 Pa or less. A subsequent atmospherepressure in the heating furnace was adjusted and density and flow rateof nitrogen and formic acid gas to be supplied to the heating furnacewere adjusted. More specifically, heat was applied with conditions of arate of temperature rise of 45° C./min, preheat of 195° C. (6 minutes),and the maximum of 260° C. (1 minute). The microbump was provided withpressure by the pressure application member and a smooth surface wasformed. In this manner, the microbump according to Example 1 wasobtained.

The microbump that was formed using the pressure application member of0.002 μg/μm² per cross-sectional area of the microbump was Example 2.The microbump that was formed using the pressure application member of0.003 μg/μm² per cross-sectional area of the microbump was Example 3.The microbump that was formed using the pressure application member of0.01 μg/μm² per cross-sectional area of the microbump was Example 4. Themicrobump that was formed using the pressure application member of 0.03μg/μm² per cross-sectional area of the microbump was Example 5. Themicrobump that was formed using the pressure application member of 0.06μg/μm² per cross-sectional area of the microbump was Example 6. All ofthe other conditions of Examples 2 to 6 were the same as those ofExample 1. In addition, the microbump that was formed by inserting a30-μm spacer made of SUS316 between the pressure application member andthe substrate was Example 7. In Example 7, the pressure applicationmember of 0.03 μg/μm² per cross-sectional area of the microbump wasused. All of the other conditions of Example 7 were the same as those ofExample 1.

Comparative Examples 1 to 7

The microbumps according to Comparative Examples 1 to 7 were formed byapplying heat in the atmosphere. In Comparative Example 1, the pressureapplication member of 0.001 μg/μm² per cross-sectional area of themicrobump was used. In Comparative Example 2, the pressure applicationmember of 0.002 μg/μm² per cross-sectional area of the microbump wasused. In Comparative Example 3, the pressure application member of 0.003μg/μm² per cross-sectional area of the microbump was used. InComparative Example 4, the pressure application member of 0.010 μg/μm²per cross-sectional area of the microbump was used. In ComparativeExample 5, the pressure application member of 0.03 μg/μm² percross-sectional area of the microbump was used. In Comparative Example6, the pressure application member of 0.06 μg/μm² per cross-sectionalarea of the microbump was used. In Comparative Example 7, the pressureapplication member of 0.10 μg/μm² per cross-sectional area of themicrobump was used. All of the other conditions of Comparative Examples1 to 7 were the same as those of Example 1.

(Evaluations)

The height of the microbumps of Examples and Comparative Examples waspresented in “Microbump Height (μm)” of FIG. 17. Among Examples andComparative Examples, those with a void that was reduced after refloware provided with “∘” and those with a void that was not reduced areprovided with “x” in “Void” of FIG. 17. Among Examples and ComparativeExamples, those with the microbump that did not fall over after thepressure application member was removed from the microbump after refloware provided with “∘” and those with the microbump that fell over areprovided with “x” in “Electrode Falling Over” of FIG. 17.

As presented in FIG. 17, in Examples 1 to 6, an effect of void reductionwas seen and no microbumps fell over. However, in Example 6, “Δ” wasprovided because molten Sn flew into the electrode pad. In Example 7,providing the spacer makes the height of the bump equal to the thicknessof the spacer, thereby having an effect of prevention of beingexcessively pushed. Accordingly, in comparison with Example 6, Example 7indicates that the molten Sn was prevented from flowing to the electrodepad. On the other hand, Comparative Examples 1 to 6 indicate that thevoid reduction had no effect. This is presumably because the oxide filmformed on the surface of the microbump has an effect of making themicrobump hard to deform and the oxide film with hard surface blocks thefluidity of inside. In addition, Comparative Example 7 indicates thatthe microbump fell over because of the excessive weight of the pressureapplication member.

Examples 8 to 11

As Example 8, a semiconductor chip that includes a microbump as followswas produced. First, a substrate was provided with Cu plating, Niplating, and Sn plating using an electrolytic plating process. Afterthis was arranged in a heating furnace, an atmosphere pressure in theheating furnace was adjusted and density and flow rate of nitrogen andformic acid gas to be supplied to the heating furnace were adjusted.This caused a sample of the semiconductor chip on which a plating filmwas molten and the microbump was formed to be created. The Cu platinglayer is 17 μm high, the Ni plating layer is 3 μm high, the microbump is15 μm high, and the microbump is 35 μm in diameter. This sample and apressure application member were prepared. The pressure applicationmember was an Si wafer that includes an SiO₂ film. The Si wafer wasmounted on the microbump so that the SiO₂ surface contacted themicrobump. The weight of the pressure application member was 0.0005μg/μm² per cross-sectional area of the microbump. It should be notedthat the spacer as presented in FIG. 8 was not provided. After thesemiconductor chip in a state where the pressure application member wasmounted thereon was arranged in the heating furnace, inside of theheating furnace was vacuumed to 5 Pa or less. A subsequent atmospherepressure in the heating furnace was adjusted and density and flow rateof nitrogen and formic acid gas to be supplied to the heating furnacewere adjusted. More specifically, heat was applied with conditions of arate of temperature rise of 45° C./min, preheat of 195° C. (6 minutes),and the maximum of 260° C. (1 minute). The microbump was provided withpressure by the pressure application member and a smooth surface wasformed. A semiconductor chip that includes a microbump like this wasprepared, and three semiconductor chips were laminated and bonded toeach other. It should be noted that the number of times of reflow was 1at the time of bonding, and the reflow was carried out in theatmosphere. The lamination of the semiconductor chips obtained in thismanner was Example 8.

One in which reflow was carried out in an atmosphere of nitrogen andformic acid at the time of bonding the semiconductor chips to each otherwas Example 9. One with 5 semiconductor chips laminated was Example 10.One with 5 semiconductor chips laminated in which reflow was carried outin an atmosphere of nitrogen and formic acid at the time of bonding thesemiconductor chips to each other was Example 11. All of the otherconditions of Examples 9 to 11 were the same as those of Example 8.

Comparative Examples 8 and 9

One with the microbumps with no smooth surface formed thereon overlaidwas Comparative Example 8. One with 5 semiconductor chips laminated andwith the microbumps with no smooth surface formed thereon overlaid wasComparative Example 9. All of the other conditions of ComparativeExamples 8 and 9 were the same as those of Example 8.

(Evaluations)

In order to evaluate mounting accuracy of the microbump, a position gapof the center of the microbump of the first and second semiconductorchips when the third semiconductor chip was overlaid was measured. AmongExamples 8 to 11 and Comparative Examples 8 and 9, those with a positiongap of less than 5 μm are provided with “∘” and those with 5 μm orgreater are provided with “x” in “Lamination Accuracy” of FIG. 18. Inorder to measure a separation mode of the microbump, the substrate andthe substrate were separated. Among Examples 8 to 11 and ComparativeExamples 8 and 9, those with fracture inside the microbump are providedwith “∘” and those with separation or crack on the interface between themicrobump and the Ni plated layer are provided with “x” in “BumpSeparation Mode” of FIG. 18. In order to evaluate bonding accuracy, amisalignment of the center of the microbump after molten and bonded wasmeasured. Among Examples 8 to 11 and Comparative Examples 8 and 9, thosewith a misalignment of less than 5 μm are provided with “∘”, thosebetween 5 μm and 10 μm are provided with “Δ”, and those of greater than10 μm are provided with “x” in “Bonding Accuracy” of FIG. 18.

In Comparative Example 8, the bottom chip was misaligned when the thirdchip was overlaid. In other words, Comparative Example 8 indicates a lowlamination accuracy and accordingly has a reduced bonding accuracy. InComparative Example 9, bonding in a one-by-one basis improved thelamination accuracy and the bonding accuracy. However, ComparativeExample 9 indicates that repeated reflow resulted in growth of the alloylayer of Ni and Sn, thereby reducing the strength of the bonded portion.Example 8 indicates that there is little misalignment when themicrobumps are overlaid because they have the smooth surface, and thusthe bonding accuracy is high. In Example 9, the oxide film is removed bycarrying out reflow in a reducing atmosphere, and the bonding accuracywas further improved due to the effect of self alignment of surfacetension of molten Sn. Examples 10 and 11 indicate that there is littlereduction in the strength of the bonded portion because reflow iscarried out once.

1 . . . semiconductor chip, 2 . . . lamination, 11 . . . substrate, 12 .. . conductive portion, 13 . . . microbump, 13 a . . . smooth surface,21 . . . pressure application member, 22 . . . void, 23 . . . oxidefilm, 26 . . . spacer.

What is claimed is:
 1. A method for producing a semiconductor chip that includes a substrate, a conductive portion formed on the substrate, and a microbump formed on the conductive portion, comprising: a smooth surface formation process of forming a smooth surface on the microbump, and the smooth surface formation process includes a heating process of causing a reducing gas to flow in an inert atmosphere into a space where the semiconductor chips are arranged and heated at or higher than a temperature of a melting point of the microbump, and in the heating process, a pressure application member is mounted on the microbump and among principal surfaces of the pressure application member, a principal surface that contacts the microbump is a flat surface.
 2. A method for producing a semiconductor chip according to claim 1, wherein in the heating process, a pressure application member is mounted on a plurality of the microbumps, and among principal surfaces of the pressure application member, a principal surface that contacts a plurality of microbumps is a flat surface.
 3. A method for producing a semiconductor chip according to claim 1, wherein as the reducing gas, carboxylic acid is applied.
 4. A method for producing a semiconductor chip according to claim 1, wherein a weight of the pressure application member is between 0.0005 μg/μm² and 0.1 μg/μm² per cross-sectional area of the microbump.
 5. A method for producing a semiconductor chip according to claim 1, wherein a spacer that has a certain thickness is arranged on the substrate and the pressure application member is pushed to contact the spacer.
 6. A method for producing a semiconductor chip according to claim 5, wherein on the substrate, a microbump arrangement area, in which a plurality of the microbumps are aligned, is set, and the spacer is arranged at an edge portion of the microbump arrangement area.
 7. A method for producing a semiconductor chip that includes a substrate, a conductive portion formed on the substrate, and a microbump formed on the conductive portion, comprising: a heating process of causing a reducing gas to flow in an inert atmosphere into a space where the semiconductor chips are arranged and heated at or higher than a temperature of a melting point of the microbump, and in the heating process, a pressure application member is mounted on the microbump, and after the heating process, the pressure application member is removed from the microbump. 